Cutting tools for performing metal working operations generally comprise a cutting insert having a surface terminating in a cutting edge and a holder formed with a seat adapted to receive the cutting insert. The cutting insert is clamped within the holder in a position so that the cutting edge of the insert engages a workpiece to remove a chip of metal during machining operations such as turning, boring, profiling, milling, threading and grooving. If the chip is allowed to form a continuous length, it tends to wrap around the cutting insert, tool holder and/or workpiece. Thus, periodic interruptions of the machining operation may be required to remove the impacted or bundled chips. Additionally, the shearing movement of a continuous chip against the cutting insert or tool holder generates intense heat which may result in the formation of craters on the exposed surfaces of the cutting insert. Once these craters become deep enough, the cutting insert may be subject to cracking and failure. Thus, it is preferable that the chip be broken into small segments when sheared from the workpiece.
Prior attempts at breaking chips have included the use of a high velocity stream of fluid directed across the exposed surface of the cutting insert and beneath the chips to break the chips into small segments. This approach is disclosed in U.S. Pat. Nos. 4,695,208 and 4,621,547, both to Yankoff.
Yankoff's '208 patent discloses a tool holder which comprises a support bar formed with a C-shaped cavity. A mounting block, which includes a seat adapted to receive the insert, is secured within the C-shaped cavity. A clamping block is mounted within the cavity atop the mounting block by means of a machine screw which engages a beveled edge formed in the clamping block. The clamping block functions both to clamp the insert within the mounting block seat, and to direct a jet of high velocity fluid across the top surface of the insert for breaking chips sheared from the workpiece into small lengths.
To deliver fluid to the clamping block, the support bar is formed with a fluid passageway connected at one end to an exterior fluid delivery line and terminating at the side wall of the C-shaped cavity. An O-ring is fitted over the terminal end of the connector passageway. The clamping block is also formed with an internal passageway which terminates at a discharge orifice. The discharge orifice is positioned to direct a jet of high velocity fluid at the chip of metal being removed from the workpiece to break the chip into small segments. With the clamping block mounted in position within the cavity, the internal passageway of the clamping block engages the O-ring at the end of the fluid passageway in the support bar. Fluid is thus transferred between the support bar and clamping block.
A number of problems have been encountered with the tool holding device described in the '208 patent. First, because the clamping block is secured along its bevelled edge, it tends to cock to one side during machining operations so that a gap forms between the side wall of the C-shaped cavity and the clamping block. When system pressures in excess of 1,500 psi are reached, the O-ring sealing the connection between the fluid passageway in the support bar and the internal passageway in the clamping block disintegrates. Without the O-ring seal, there is a marked decrease in the velocity of the fluid discharged from the discharge orifice since much of the fluid passes through the gap between the support bar and clamping block.
In addition, there is a problem with the terminal end of the bevelled edge of the clamping block notching the tapered head of the set screw used to secure the clamping block. When the terminal end of the bevelled edge penetrates too deeply into the tapered head of the machine screw, it "locks" the machine screw so that it cannot be removed. Thus, some difficulty has been experienced in indexing the cutting insert.